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Iowa and Alaska class gunnery charts


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#1 Ken Sloan

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Posted 09 March 2013 - 04:54 AM

I didn't see this covered anywhere, but are there charts for the Iowa class 16 inch guns and the Alaska 12 inch guns? They are claimed to be significantly superior to their predecessors. I know they are very late war ships but it would be nice to have the charts to run "what if" engagements.

Thanks

#2 Dave Franklin

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Posted 09 March 2013 - 03:22 PM

Regarding the USN 16" guns, the USN 16" is already superior to both the RN and IJN. For example, both the USN and the RN 16" penetrate BA+ to 12000yds, but the IJN only penetrates BA+ to 9000yds. The USN 16" penetrates BA out to 21000yds and hits at 1+ out to 24000yds, while the RN only penetrates BA out to 18000yds and only hits 1+ out to 21000yds. The powers-at-be can correct me if I'm wrong, but the USN 16" is supposed to be representative of the guns on the North Carolinas, South Dakotas and Iowas, with their heavier shell. The 16"/50s on the Iowas might have had a better theoretical range, but with the low odds of hitting, I'm not sure it's worth worrying about. What's really missing is the 16" on the Maryland/Colorados.

Similarly, with a listed maximum range of 39000yds, the USN 12" is the gun on the Alaskas. What's really missing is the 12" for USS Arkansas.

Dave

P.S. I would ask the question, now that I looked at it, why is the RN 16" gun, presumably supposed to be that for the Nelsons, better than the IJN for the Nagatos? The IJN shell was heavier...

#3 Ken Sloan

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Posted 09 March 2013 - 05:36 PM

My concern is less about range and more about penetration. It is my understanding is that the longer 16 inch guns on the Iowa class had a much higher muzzle velocity. Like how the Sherman and Panther had the same 75mm but the Panther was so much more powerful. I've even heard that the 16"/50 had similiar performance to the IJN 18".

The 12" on the Alaska class could penetrate 18" of armor at 10k yards. That's BA+ penetration.

Maybe one day we will get a 1945 supplement. It would be nice to have all the tables and the ship cards for that period.

Ken

#4 Cpt M

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Posted 09 March 2013 - 10:21 PM

My concern is less about range and more about penetration. It is my understanding is that the longer 16 inch guns on the Iowa class had a much higher muzzle velocity. Like how the Sherman and Panther had the same 75mm but the Panther was so much more powerful. I've even heard that the 16"/50 had similiar performance to the IJN 18".

The USN CRTs are optimized for the early to mid war period (when most of the major surface actions occurred). Consequently, the much later 16" Mk7 and 12" Mk 8 are not reflected in the table (neither of these weapons figured in any surface action). That said, a modification to the penetration values for hypothetical late war actions could be made on a scenario specific basis (for more on this see below).

The 12" on the Alaska class could penetrate 18" of armor at 10k yards. That's BA+ penetration.

The penetration mentioned is based on both empirical data and tables derived by the USN. Both are, essentially, proving ground numbers. While useful for comparing one gun to another, such data are not useful for combat results as these are almost always derived under ideal conditions (new guns with hand picked charges fired at stable, vertical plates under ideal weather conditions). Combat conditions rarely present such an ideal situation, however. Charges are rarely ideal, the weather conditions are whatever they may be and the shells themselves are striking a moving (in all three axes) target. Consequently, all peneteration data in the CRTs have been discounted by a preset percentage to account for real world conditions vs the ideal proving ground conditions. While the 12"/50 Mk 8 may have penetrated 18" at 10000 yds on the range (or ascribed such performance by empircal calculation), it is highly improbable that such performance would be repeated in combat.

Maybe one day we will get a 1945 supplement. It would be nice to have all the tables and the ship cards for that period.

Given that only six ships (the four Iowas and two Alaskas) are impacted and that all would only feature in very late war scenarios, I doubt a specific update would be warranted. That said, as scenario specific modifications, the following penetration values could be used:

For the 16"/50 Mk 7 (Iowas and aborted Montanas only): Change the 15000 yd row to BA+ (from BA) and the 24000 yd row to BA (from BB).

For the 12"/50 Mk 8 (Alaskas only): Change the 18000 yd row to BB (from BC), change the 24000 yd row to BC (from BD),

These adjustments assume a reduction of the 'book' value penetration in line with the methodology used for the remainder of the CRT penetration values (and, in fact, may be a bit generous).

#5 Cpt M

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Posted 09 March 2013 - 10:33 PM

P.S. I would ask the question, now that I looked at it, why is the RN 16" gun, presumably supposed to be that for the Nelsons, better than the IJN for the Nagatos? The IJN shell was heavier...

The RN 16" is the 16" Mk I as mounted by Nelson and Rodney. Based on best information available, it was superior to the IJN's 16" shell as it was of later design. (The RN 16" shell was purposely designed as a light shell. While its performance fell below what was expected, it was still superior to the older IJN design. Shell weight is only one of several factors in penetration performance.).

#6 Cpt M

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Posted 09 March 2013 - 11:13 PM

What's really missing is the 16" on the Maryland/Colorados.

Actually, the performance of the 16"/45 Mk 8 (Colorados class) and the 16"/45 Mk 6 (North Carolina and,South Dakota class) have very similar performance (in game terms). A redesign/reconstruction of the original 16"/45.Mk 5 guns of the Colorados allowed for a larger charge and shell. While the gun could not use the 2700 lb super-heavy shell, the 2240 lb shell used gave much better performance than the original shell. In game terms, the penetration values fall within the same parameters. Consequently, a separate column would not be indicated (the values for the 16"/45 Mk.8 and 16"/45 Mk 6 are used on the USN CRT).

#7 Dave Franklin

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Posted 10 March 2013 - 08:24 PM

"For the 12"/50 Mk 8 (Alaskas only): Change the 18000 yd row to BB (from BC), change the 24000 yd row to BC (from BD)."

So then you're saying the USN 12" IS for the Mk 7 on USS Arkansas!? What references do you have where that gun can shoot out to 39000yds?

Navweaps indicates the elevation on the mount went to +15deg, and the max range at 24000yds.

I might buy the assessment for the 16" guns (e.g. the upgrades for the 16"/50 Mk 7), but I disagree with your assessment of the 12" guns.

#8 Cpt M

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Posted 11 March 2013 - 09:17 PM

"For the 12"/50 Mk 8 (Alaskas only): Change the 18000 yd row to BB (from BC), change the 24000 yd row to BC (from BD)."

So then you're saying the USN 12" IS for the Mk 7 on USS Arkansas!? What references do you have where that gun can shoot out to 39000yds?

Navweaps indicates the elevation on the mount went to +15deg, and the max range at 24000yds.

I might buy the assessment for the 16" guns (e.g. the upgrades for the 16"/50 Mk 7), but I disagree with your assessment of the 12" guns.

The 12"/50 Mk 7 (used on the Wyoming class) is indeed the gun represented on the table. Arkansas, during her July, 1942 refit had her maximum elevation raised from 15 degrees to 30 degrees (inline with the same refit to the 14" gun ships). The maximum range of 24000 yds would apply pre-refit. In point of fact, the earlier gun had a superior range performance compared to the later gun due to a higher muzzle velocity (the Mk 8 was good for 22000 yds at 15 degrees while the Mk 7 was good for 24000 yds).

#9 Dave Franklin

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Posted 22 March 2013 - 12:39 PM

Well, I haven't been able to find any info in any of my reference books about Arkansas's main gun elevation being increased to 30 degrees. Wondering what your source is?

As long as we're talking about updated data for the Montanas, what about for their 5"/51s?

#10 Dave Franklin

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Posted 22 March 2013 - 01:22 PM

Oops, meant 5"/54s...

#11 Cpt M

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Posted 22 March 2013 - 11:01 PM

Well, I haven't been able to find any info in any of my reference books about Arkansas's main gun elevation being increased to 30 degrees. Wondering what your source is?

The source is an USN report of the Arkansas' post refit shakedown that I acquired while doing research at the National Archives outside DC. It detailed many of the upgrades made during the refit plus some deficiencies that needed to be addressed.

#12 Cpt M

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Posted 22 March 2013 - 11:07 PM

Oops, meant 5"/54s...

Since this gun didn't go to sea until after the war (first aboard the Midway class carriers in late 1945), it wouldn't be included in the USN CRT. And as its characteristics are considerably different from any of the other USN 5" guns, I would be hard pressed to even guess what values to assign it.




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